In recent years, in a liquid-crystal display device or the like, a polarizing film has been used as a thin polarizing plate that is obtained by absorbing an iodine compound onto a polyvinyl alcohol (PVA) film and drawing and orienting the result to express absorption linear dichroism. To ensure mechanical strength, heat resistance, and humidity resistance, both surfaces of the polarizing film are interposed between transparent films made of triacetyl cellulose (TAC) or the like, and hard coating is performed thereon to prevent flaws, attachment of fouling, and others.
Of light entering the polarizing film, light of polarizing components not passing therethrough is absorbed onto the polarizing film and is dissipated as heat to the outside of the film. For this reason, at the time of irradiation of strong light, the temperature of the film is increased by heating to disadvantageously degrade polarization properties. This is due to heat resistance of an organic material itself, and substantive improvement is difficult.
To address this problem, a polarizing plate configured only of a completely inorganic material is used. What is typical as a thin polarizing plate is a polarizing glass and a wire-grid polarizing plate. The polarizing glass is formed of metal island-shaped fine particles deposited in the glass, and is caused to express absorption linear dichroism by anisotropy of plasma resonance absorption of the fine particles. While the polarizing components not passing through are absorbed, the plate is configured of an inorganic material, and therefore has a high heat resistance.
On the other hand, the wire-grid polarizing plate has a wire grid made of fine metal wires having a period equal to or smaller than the wavelength of light formed on a front surface of a substrate (refer to Patent Document 1). In this wire-grid polarizing plate, polarizing components not passing through are reflected due to plasma oscillation of free electrons, and therefore there is a merit that incident light can be more effectively used.
Also, as a type similar to the wire grid, there is a fine-particle-type polarizing plate formed with oval metal fine particles arranged on a front surface of a substrate (refer to Patent Document 2). This uses plasma resonance absorption of fine particles and, unlike the wire-grid polarizing plate, polarizing components not passing through are absorbed. Thus, for example, to prevent a temperature increase or degradation of the liquid-crystal panel due to reflected light from the polarizing plate, this plate is used on an emission side of the liquid-crystal panel.
These polarizing plates made of an inorganic material has no problem in degradation in properties due to heat resistance as seen in an organic polarizing film, and has been used as a polarizing plate for liquid-crystal projectors irradiated with strong lamp light.